Dual Row Connector for Low Profile Package

The present invention relates to a dual row printed circuit board connector which receives and supports printed circuit board modules known as daughter boards and effects an interconnection thereof to a further common printed circuit board known as a mother board, with an axis of mounting relative thereto which is substantially less than the traditional 90 degrees, to thereby provide an electronic package of lower profile. The connector housing is molded in a fashion to provide a structural integrity necessitated by the need to support the weight of daughter boards and the components thereon.

Edge connectors for printed circuit boards are well known and widely used as the principle means of interconnecting electronic subassemblies which form functioning devices such as computers, telecommunications gear, test apparatus and the like. Such connectors are often termed "PC board connectors" or edge card connectors and are typically comprised of plastic material formed into what is known as a housing and made to contain a series of electrical contacts stamped and formed and plated to interconnect the individual components on a daughter board through pads on the edge thereof to circuits in or on a mother board via tabs or posts soldered thereto. The contacts of the connector generally are arranged to have spring portions which allow the daughter boards to be plugged in or removed therefrom. This arrangement permits replacement, repair or changes in components on the daughter boards to be done apart from the location of the mother board. It further allows the different circuits and arrangements of components to be individually packaged so as to be separately processible in production.

The concept of the use of printed circuit boards to mount components as on daughter boards and to be pluggably interconnected as on mother boards has indeed become one of the major means of providing electronic circuits of all kinds, and the connectors used therefor are widely employed in industry. U.S. Pat. No. 4,077,694 shows an example of an edge card connector which has two rows of terminals which contact both sides of a daughter board, and U.S. Pat. No. 3,601,775 shows a similar arrangement for contact of one side of a board.

In general, the printed circuit board connector serves a first function of allowing the mounting of contacts on appropriate centers in an appropriate orientation to make contact with pads on daughter boards on the one hand, and contact with pads or holes in a mother board interconnected to circuits thereon. A second function performed by the connector is to physically mount the daughter board in a stable and reliable manner so that it will not be unintentionally displaced or disturbed in use. It is particularly critical that the daughter board not be allowed to move through vibration or other physical stimuli relative to the electrical interface with the connector contact, as this can cause circuit intermittence as well as a deterioration of the contact interfaces due to fretting corrosion or the like. The connector housing which is typically of a dielectric material suitably moldable, contains card or board guides so as to accurately position a daughter board relative to a mother board so that all interconnections are maintained properly in both a physical and dimensional sense and in terms of suitable electrical isolation.

As a general rule, card guides or other such structures are employed to help align daughter boards during insertion into printed circuit board connectors and more importantly, to support such boards so that the weight thereof will not overly stress the contacts contained in such connectors or the housings of the connectors, particularly with respect to the weight of the components mounted on daughter boards. This weight is not always static in that electronic packages are frequently subjected to movement in a variety of attitudes, vibration, shock as by dropping, or sudden changes in velocity or acceleration; all expressed in at least some part in a variety of compressional, sheer and tensional forces on the connector housing, as well as on the contacts therein.

The advance of semiconductor technology has resulted in development of chip carriers which comprise substrates on which the chips are mounted and electrically connected by fine wires. The substrates are plugged into sockets having resilient contact members which make contact with surface traces on the substrate. See, e.g., U.S. Pat. No. 3,753,211, which discloses a socket having terminals for contact with opposed edges. In some applications, as where as board space is at a premium, it is desirable to connect the substrate edge to the board. One such application is the use of edge mounted memory modules in the form of single in-line memory modules. Standard card edge connectors cannot be simply downsized to meet the requirements of a substrate to board connection, known as a level two connection. This connection is relatively much smaller and requires simple, compact contacts on a much smaller spacing. As such, variations in board thickness and board warpage are much more likely to deflect contact means beyond the elastic limit, which would adversely affect contact pressure and thus the integrity of the electrical connection of future substrate insertions.

Given that the single in-line memory modules have a tendency for the boards to warp, the housing which carries the electrical contacts must be designed to optimally resist the warpage of the housing also. Furthermore with the anticipated vibration of the connectors and modules, it is important that the connector to include a latching means to detect the full insertion of the module into the socket and to prevent the withdrawal of the module during vibration. Further considerations to the design of the connector relate to the attempt to increasing requirement of optimizing the real estate usage of the board while maintaining a small envelope and low profile in which the assembly resides.

The present invention relates to a printed circuit board connector which electrically interconnects the circuits on printed circuit board modules or single in-line memory modules to circuits on a common board, wherein the axis of memory module insertion and withdrawal is oblique to the plane of the common board. In an illustrative embodiment, the angle between the plane of insertion and withdrawal and the plane of the common board, is on the order of 25 degrees. This allows a lower profile package than is possible with the typical 90 degree arrangement between the plane of insertion withdrawl of a memory module and the plane of the common board. The connector housing which is of a dielectric and insulating material, includes multiple rows of contacts contained within housing portions which form slots for card support and integrally therewith, board support and latching structures on each end of such rows with the rows and the end portions interconnected by a common web of plastic material. The web which joins the rows and end portions is essentially free of surfaces which would obstruct the flow of plastic during molding of the connector and provides a one-piece integral connector structure which is rigid and sufficiently strong to accommodate the concept of having daughter boards inserted at an angle to a mother board. The central web further allows a flow of plastic during molding which has been discovered to avoid knit lines in the plastic resulting from circuitous flow paths in the mold for the connector. The web thus acts as a large and relatively broad sprue-like medium which becomes a structural part of the connector. The presence of the web and its relationship to the portions of the connector which form the contact rows and the end support structures, in conjunction with the choice of the molding injection port and the flow pattern of plastic, provides a housing of improved rigidity and strength.

FIG. 1a is a side view showing a series of daughter boards mounted into edge card connectors, in turn mounted on a mother board in accordance with the practice of prior art packaging.

FIG. 1b is an isometric view of the ensemble represented in FIG. 1a.

FIG. 2a is a side view of the daughter boards mounted in edge card connectors, in turn mounted on a mother board in accordance with the improvement of the invention.

FIG. 2b is an isometric view of the structure represented in FIG. 2a.

FIG. 3 is an isometric view of the dual row connector of the invention, somewhat enlarged relative to the showing in FIGS. 2a and 2b, to depict the various details of the connector housing and the arrangement of contacts therein.

FIG. 4 is a plan view of the connector as shown in FIG. 3.

FIG. 5 is an end view of a section of the connector shown in FIGS. 3 and 4.

FIG. 6 is an isometric view of the contact shown in the connector of the invention.

FIGS. 1a, 1b and 2a, 2b are now referred to to explain the invention with an enumeration intended to relate the common elements of the prior art to those of the invention as an aid in comprehension. In these four figures, the common elements or features have common enumeration.

First referring to FIGS. 1a and 1b, the ensemble there shown includes a common mounting printed circuit board depicted as M which is to be understood to have a series of conductive traces thereon shown as T which form the interconnecting circuit paths relative to the electronic entity being served by the overall package, shown in phantom as P. It is to be understood that additional circuit paths such as T may be interspersed in the several layers of M or indeed carried on the top surface of M as well. Power, ground and signal paths are typically brought to M via IO connectors shown connected to one edge of M in FIGS. 1a and 1b. A series of memory modules labeled D are shown in FIGS. 1a and 1b to contain a series of electronic components C, typically integrated circuit packages and those electronic function devices which are necessary such as resistors, capacitors, inductors, diodes and the like, which form the different circuit subassemblies of the overall package. These boards or cards are plugged into edge card connectors shown as H which contain contacts similar to those to be described, in turn soldered into the mother board M. The boards D are typically inserted or withdrawn along axes shown as I in FIGS. 1a and 1b, and when inserted the boards D form an overall profile in the elevation, generally shown as P in FIG. 1a, and in perspective in FIG. 1b.

FIGS. 2a and 2b depict similar elements with similar functions to that just described, with the difference being that the housings H are dual row housings intended to take two memory modules and these housings have an axis of insertion I oblique to the plane of the mother board M. In the FIGS. 2a and 2b, this axis is shown in an illustrative manner at about 25 degrees relative to the plane of M. As can be discerned, the positioning of the memory modules D in such fashion changes the outside profile of P in a significant fashion, particularly with respect to the height thereof. If the only support given to the memory modules D was indeed that from the housings H and if the orientation of the package with respect to gravity or movement or other stresses were always as depicted in the FIGS. 1a-2b, the need for additional strength and additional support provided by the housings of the invention relative to the prior art approach would need no additional comment. It is, however, to be understood that while much of the use of the invention package is intended for computer and communication packages or perhaps in computer or appliance applications wherein the packages are always or almost always oriented as shown in the FIGS. 1a-2b, it is contemplated that other attitudes and orientations will be experienced at least in shipping or in those cases where the packaging scheme is employed in vehicles and craft which experience a wide variety of movement, acceleration, velocity, and attitude. To this end, the memory modules D may very well be associated with card guide structures not shown but which support along the edges or the rear thereof, not only with the weight of the boards but the weight of the components thereon; all tied together with the mother board which is incidentally supported by the overall package structure. Even with card guides, supports, clamps or the like, it can be discerned by comparing FIGS. 1a-1b to FIGS. 2a-2b, that their fundamental differences of structure require greater strength in the latter than in the former.

Referring now to FIGS. 3-5, the housing of the invention heretofore referred to as H is shown in detail to be a one-piece element 10 having a first row shown as 12 and spaced thereform, a second row 14. These rows contain a series of electrical contacts 16 and 18 mounted within the housing walls. The profile of the contacts can best be seen from FIGS. 5 and 6 to include as is shown with respect to contact 18 in FIG. 6 an upper spring element 20 and a lower bifurcated spring element 22, oriented to contact and bear against the upper and lower surfaces of a memory module inserted therebetween. A memory module D is shown in phantom in FIG. 5, consistent with the showing in FIGS. 2a and 2b. The contacts such as 18 have a tail shown as 24 which in one embodiment extends through an aperture 26 in housing 10 as is shown in FIG. 5 to be inserted into the hole in a mother board, such hole being shown as 40 and eventually, soldered to the conductive traces on the surfaces or within the mother board M. As can be seen from FIGS. 3 and 5, the contacts are held in an orientation which is common to a given row and to the axis of insertion shown as I as heretofore mentioned. Details of the contacts such as 18 are covered in U.S. patent application Ser. No. 800,181 filed Nov. 11, 1985 in the name of Roger L. Thrush and assigned to the assignee of the present invention, the substance of that disclosure being incorporated herein by reference. Reference is made to such application for additional details relative to a preferred embodiment of contact, it being understood that contacts having the same function but of different geometries are contemplated. The critical aspects of the contact relate to the fact that the U-shaped elements 20 and 22 have sufficient spring characteristics to provide adequate normal forces for effective contact with the pads on the memory module D without being overstressed or permanently deformed in normal use. Additionally, it is important that the interior surfaces of the elements 20 and 22 be given a surface finish appropriate to the particular spring design and the particular duty, including numbers of insertions and environment of both inventory and use contemplated. Similarly, the surface of the post 24 should be coated or plated or otherwise made compatible with the particular process of interconnection to the mother board circuit paths as by wave soldering, flow soldering, or other such processes.

It is to be realized that the contacts such as 18 and accordingly the housing chambers for the rows 12 and 14 are in practice quite small, the row cavities being typically on centers of 0.1 inches, which makes the various dimensions, thicknesses, wall sections and the like, quite small and relatively fragile. The nature of these parameters emphasizes the need for providing adequate board and contact support.

As part of the strengthening of the contact housing 10, the individual cavities for the contacts are defined by wall sections 30 (FIGS. 3 and 5) and extend along the sides of the contacts 18, the wall sections being integrally molded with upper and lower plastic portions shown as 15 and 17, respectively, in FIG. 5. Additionally, ramparts shown in FIG. 4 as 32 are brought out of the vertical wall sections 30 periodically toward the center area of the housing 10, and as shown in FIG. 5, ramparts 34 are included on the opposite side of a web 60. The ramparts 32 serve the function of strengthening and guiding the memory module during insertion in the event that there is some bow or sag in the center thereof. As shown in FIGS. 3 and 5, similar guiding structures 33, also termed ramparts, are located with respect to the row 12 in FIGS. 3 and 5.

As can be seen best in FIG. 5, the contacts such as 18 are anchored within the cavities associated with their respective rows by virtue of the tab or post elements 24 being inserted through the rear wall aperture 26 and then deformed downwardly in the position as shown. This serves to snug the contacts into position and hold them there, centered properly relative to insertion of the memory modules.

As can best be seen in FIG. 3, there is included at either end of the rows 12 and 14 a strengthening and guiding structure shown as 42 which includes interiorly thereof, a groove 44 which serves as a PC board guide and support element, catching the edges of a PC board and thus centering the board relative to its pads with the contacts 16, 18 in a given row. As will be observed from FIG. 4, a printed circuit board is shown in phantom inserted in the upper row 14 of the connector housing 10. At the leading edge of the groove 44 are beveled face portions shown as 46 which help guide the insertion of a printed circuit board. Also shown in FIG. 3 is a latch structure 48 formed integrally from the molding of the housing which is beveled and has a projection at 50 intended to fit within the hole 51 of a printed circuit board to latch such board into position in the housing. This detail is shown in FIG. 2B and in phantom in FIG. 5. Directly in alignment with the latch structure 48 is an aperture shown as 52 in FIG. 3, which extends through the housing sidewall allowing the latch structure to be molded by a straight action closure of the molding surfaces, apertures 52 defined by retracting pin portions of the mold which are initially inserted through the housing to define the rear surface of 50. The element 54 is intended to show the relatively thick portion of the end guiding projection 42 which provides structural support for the memory module.

The housing 10 includes at each end of each row a similar structure to that just described with respect to 42, essentially reversed on the left side of the connector and modified on the lower part of the connector as at 55 for the purpose of establishing vertical surfaces shown as 57 for automatic handling as by robotic fingers. The surfaces need precise definition, and need to be flash and sprue free.

In use, the end structure such as 42 functions to guide, position and latch a printed circuit board into position within the rows 12 and 14. U.S. patent application Ser. No. 800,181 as aforementioned shows these features in greater detail. To remove a board from the connector, it is necessary to depress the latches as at 50 so that the projection surfaces clear the edge of the holes in the board and the board can be withdrawn. As will be discerned from FIG. 5, the plane of axis I is at an angle of roughly 25 degrees from the plane of the mother board M. This angle and therefore the axis of withdrawal, may be varied in accordance with packaging needs but suffice to say, it is different from and substantially less than the normal 90 degree angle of intersection of the planes of memory modules and mother boards.

Housing 10 includes as a further detail, four posts 64 which are inserted through holes in the mother board to position the connector housing initially prior to soldering of the tabs 24 thereto. The projections 64 may be optionally of different diameters to match different diameters in the mother board so as to polarize or orient the mounting of the housing in such board. Also optionally, after insertion of the housing 10 and the terminal post 24 through holes in the mother board, the posts 64 may be deformed by heat and/or pressure to mechanically lock the housing 10 to the mother board, the intention being to reduce the strains placed on the solder joints between the tabs 24 and the circuit traces of the mother board, the posts partially accommodating such mechanical strains during insertion, withdrawal of memory modules and during the life of the electronic package served by the connector.

In accordance with the invention, the two connector rows 12 and 14 are interconnected by a web 60 shown in FIGS. 3, 4 and 5, which in conjunction with the ramparts heretofore described and the end elements of 42 and 62, create a structure of considerable strength and integrity, tying all of the various elements of housing 10 together in one homogeneous mass of plastic material. As heretofore mentioned, the ability of the connector housing to support memory modules at an angle relative to the mother board, is enhanced by the particular structure embraced by the invention.

As a further aspect of the invention, reference is now made to FIG. 3 and to a series of arrows labeled MP which refer to mold parting axes. Three such axes are shown, one axis labeled MP1 coming off the face of the connector parallel to the axis of board insertion I, a second axis labeled MP2 parallel to MP1 but in an opposite direction and coming off the rear face of the connector, and finally, a third axis labeled MP3 parallel with the mounting surface of the connector and with the posts 64. Shown in FIG. 3 is a further axis labeled PI which is the axis of plastic injection during molding, there being dotted in and labeled F, plastic flow lines indicative of the flow of plastic during an injection cycle. The connector housing 10 is molded in one cycle as one integral mass of plastic and it has been discovered that the cavity which forms the structure of web 60 by being made continuous and utilized as an internal sprue for accommodating the flow of plastic, allows a fill of the details of the housing without knit lines or voids in mold filling. Put another way, holes or apertures or other reliefs in 60 for whatever purpose that might impede such flow, have been found to cause molding complexities including longer cycle times and improper fill, not only adjacent to such discontinuities, but in fine details such as the ramparts and/or the walls such as 30 as shown in FIG. 3.

In practice, the interior surfaces of the molds, which can be discerned from an examination of FIGS. 3, 4 and 5, are closed to form a volume of the shape indicated with injection being made at one end as at the point where the arrow of PI is disposed in FIG. 3, and in FIG. 4, plastic under high pressure is injected to fill the cavity of the mold, a suitable dwell time is allowed and then the mold is opened with the first draw axis being along the directions indicated by the arrows MP1 and MP2 parallel to I; that part of the mold accommodating the undersurface and posts 64, thereafter being drawn open along axis MP3 to release the housing from the mold. Ejection of the part takes place by lifters which bear against the surfaces L as shown in FIG. 3, along the length of the connector housing. In practice, it is contemplated that without posts 64 a straight action may be used, as where rivet holes and brackets are employed. It should be noted that the molding techniques as disclosed above allows the web 60 and the latches 48 to be integrally molded within the unitary structure which defines the connector housing. As the mold parting lines are oblique parting lines parallel to the axis of the cavities, rather than perfectly perpendicular or horizontal part lines, the integral web can be formed by the passing mold dies which in conjunction with each other, form the rear wall 70 of the first row 12 and the internal contact receiving surface 72 of the second row 14, as best shown in FIG. 5. As mentioned earlier the availability of the latching structure of surface 50 is defined by retracting pins which also define apertures 52 (FIG. 3) during their retraction.

In an actual example of the invention in a preferred embodiment, the material for the housing 10 was comprised of a glass fiber reinforced thermoplastic liquid crystal polymer, of which a number are available as engineering materials from a variety of common sources. The contacts such as 18 were made of stamped and formed beryllium copper of a thickness on the order of less than 0.01 inches, having postplated gold surfaces selectively applied to the upper portions of the contacts, and having a tin leaded solder plated onto the posts 24, there being a suitable nickel underplate over the surface of the contact 18. Relative to the illustrative embodiment, the contacts were centered on 0.1 inch centers to be inserted in the holes in the memory modules which were on the order of 0.04 inches. To give an idea of size, the posts 64 were on centers of 0.5 inches relative to FIG. 5 and the length of the connector housing 10 from end to end was on the order of 3.8 inches. The ends of the latches were intended to fit within holes in the memory module approximately 0.125 inches in diameter and the contacts themselves were intended to mate with pads roughly 0.07 inches in width and similarly dimensioned in depth, placed on the edge of the memory module. Such boards were on the order of 0.05 inches in thickness.

In the foregoing description, reference has been made to printed circuit boards in the form of memory modules and mother boards which are typically formed of a variety of materials such as phenolics and epoxy. It is fully contemplated by the present invention that the structural aspects are applicable to connectors which accommodate other electronic packages of the type which may be inserted into an edge card type contact including those of a much smaller scaled-down dimension made of glass or ceramic, silica or other materials utilized for displays, memory, logic, and other such applications.

In the use of terminology, the words "board", "card", "module", and "package" have been employed to describe circuit elements which mate and unmate together to form functioning, electronic products. It is pointed out that the choice of terminology employed is consistent with the terminology used in the state of the art to which the invention relates in order to illustrate and exemplify the preferred practice of the invention, but not to restrict its scope; the appended claims being reserved to that end.